Abstract from the original SBIR Phase II This project will test human embryonic stem cell-derived 3-D retinal tissue transplanted in subretinal space of 2 animal models with photoreceptor (PR) degeneration in a longitudinal study lasting for up to 12 months. We will use a large-eye animal model of early-onset RD with a Crx mutation (Rdy Abyssinian cats) and immuno- deficient rats with PR degeneration SD-Foxn1 Tg(S334ter)3Lav (RD nude). The immediate goal is to demonstrate the survival, lamination, maturation, and structural and synaptic integration of grafts with the recipient retina, and improvement in vision by 6-12 months, and to generate standard operating procedures for transforming such technology into therapy to treat blindness caused by PR death. The overarching goal is to evaluate this technology in pilot clinical trials in patients with retinitis pigmentosa (RP), an orphan disease with fast track FDA approval. Blindness is a major health concern among Americans, affecting quality of life and with a high financial and heavy emotional burden. The two major retinal diseases associated with photoreceptor degeneration are RP and dry age-related macular degeneration (AMD). There is a critical and urgent need to find new treatments of RP and AMD based on photoreceptor replacement. The research in the past 15-20 years indicates that a piece of degenerating mammalian retina can be replaced with healthy fetal retinal tissue, which can improve vision. The research shows that grafted fetal retina will complete differentiation, synapse on the recipient retinal ganglion cell neurons, and re-establish connectivity with the visual cortex. Human fetal-derived retinal tissue supply is very limited, and its clinical use in therapy is ethically not acceptable. BioTime hypothesizes that 6-8-week old human embryonic stem cell-derived 3-D retinal tissue will integrate structurally and synaptically into the degenerating recipient retina and improve vision in animals with advanced RD. We predict that demonstrating positive therapeutic impact of hESC-3D retinal tissue grafting in a ?large eye? animal model with RD will enable us to move this technology to pilot clinical trials in RP patients. We have already developed hESC-3D retinal tissue and demonstrated that it carries a layer of RPE, PRs, second order neurons and ganglion cells, is capable of axonogenesis, synaptogenesis and becomes progressively electrically active. We also reported that it improves vision in a rat animal model with RP and blindness and activates superior colliculus. We propose to do in vivo testing in a ?large eye? animal model of RD (Rdy cats) with blindness, and in a large cohort of SD-Foxn1 Tg(S334ter)3Lav (RD nude) rats with RD to statistically evaluate the feasibility of this therapy in RP patients. ? In Aim 1 (BioTime), we will scale-up production of hESC-3D retinal tissue from cGMP-grade hESCs and evaluate several lots using FDA criteria. ? In Aim 2 (UCI), we will do subretinal grafting into blind rats and evaluate vision improvements and graft- host connectivity. ? In Aim 3 (MSU), we will do subretinal grafting into Rdy/+ cats and also evaluate vision improvements and graft-host connectivity. The results and procedures will be integrated into clinical protocols to enable clinical trials of blindness caused by PR degeneration.